One may argue that holding cash is safer than buying an index fund (or stock, ETF, mutual fund, etc), and financially that may be
true over a given period of time (for instance, the USD beat the SPY for the year of 2008).
His assertion that the models will be more correct
over longer
time periods, for example, has not been shown to be
true, so there is no good reason
give it a lot
of weight.